64 



during the two seasons the writer feels justified in drawing some gen- 

 eral conclusions. Some of these were given expression in an earlier 

 article on pages 51-64 of Bulletin No. 22 of the present series. 



It may be remembered that the writer hazarded an opinion as to the 

 probabilities that certain Northern forms would continue in similar or 

 increasing numbers as a result of protracted cool winter weather, that 

 would tend to facilitate perfect hibernation, while certain Southern 

 species, which were apparently nearly exterminated in and near the 

 District of Columbia as a consequence of the cold winter of 1899-1900, 

 would continue absent from this neighborhood, or at least that the 

 crops habitually attacked by them would not be materially affected 

 during the season of 1900. This prediction has been partially veri- 

 fied. Such Northern species as came under observation as a result of 

 their injurious abundance in 1899 continued to be injurious, as it was 

 judged they would, but certain of the Southern forms became quite 

 numerous. True, only one of these was abundant early in the season, 

 but the remainder, although extremely rare during the early part of 

 the year, became sufficiently numerous to attract rather general 

 attention late in the season. Prominent among these were the cab- 

 bage Pionea, the single species which occurred here in numbers from 

 earty in the year; the cabbage looper, which was universally trouble- 

 some to late cabbage and other cruciferous crops, and the boll worm, 

 also destructive to late crops, such as corn and tomatoes. 



As to the cause of the early reappearance of the first-mentioned pest 

 after such extreme scarcity, the only conclusion that can be reached 

 is that this was due mainly, if not entirely, to the flight of the parent 

 moths from the South either late in the season of 1899 or early in 1900, 

 or at both times. It is to be regretted, however, that the mature 

 insects were not detected at lights or in the field either in autumn or 

 spring. The cabbage looper and boll worm owe their increase proba- 

 bly to the same cause as the Pionea. 



It is now a matter of almost annual occurrence — and the season of 

 1900 was no exception — for the cotton worm, Aletia argUlacea, to fly 

 from the cotton fields thousands of miles north of their natural habi- 

 tat, a phenomenon well known to collectors, who frequently take this 

 insect at electric lights in the Northern States, and even in Canada, 

 although their larvae have not been detected north of the cotton belt. 

 This is only one of many species which have the same habit, and the 

 writer believes that the invasion of the territory about the District of 

 Columbia and northward by the three species above mentioned has 

 been made in the same way, the moths having flown northward, at 

 intervals perhaps, during the season with winds which favored this 

 flight, from localities farther south not affected to the same extent by 

 the atmospheric conditions of the winter of 1S98-99. 



A circumstance which lends color to the above expressed hypothesis. 



